Bio-degradable composite nonwoven fabric for plant cultivation

Abstract

A bio-degradable composite nonwoven fabric for plant cultivation includes a wood pulp paper sheet laminated on a bio-degradable aliphatic polyester filament nonwoven fabric, wherein the polyester filaments and the pulp fibers are entangled to each other and a plurality of spot regions which are spaced from each other, are substantially free from the pulp fibers and have a decreased distribution density of the polyester filaments of 30 to 50%, an area of 0.16 to 16 mm2 and a total area coresponding to 5 to 60% of the total surface area of the composite nonwoven fabric, are formed. The polyester filament distribution density is defined as the ratio of the total area of the polyester filaments appearing within the spot regions to the total surface area of the spot regions, determined from photographs of the spot regions.

We claim: 
     
       1. A bio-degradable composite nonwoven fabric for plant cultivation, comprising (A) a biodegradable polyester filament nonwoven fabric layer consisting essentially of a plurality of continuous filaments comprising a bio-degradable polyester which is a polymerization product of a glycol component comprising at least one aliphatic dihydric alcohol with a dicarboxylic acid component comprising at least one member selected from the group consisting of aliphatic dicarboxylic acids and hydroxyl and acetoxyl derivatives of the above-mentioned dicarboxylic acids; and   (B) a paper sheet layer laminated on the biodegradable polyester filament nonwoven fabric layer (A) and comprising wood pulp fibers, wherein (a) the continuous filaments and the wood pulp fibers are three-dimensionally entangled with each other to form a composite nonwoven fabric, and   (b) a plurality of spot regions which are spaced from each other, are substantially free from the pulp fibers, and have a distribution density of the continuous filaments of 30 to 50%, an area of 0.16 to 16 mm 2  and a total area corresponding to 5 to 60% of the total surface area of the composite nonwoven fabric, are provided in the composite nonwoven fabric, the distribution density of the continuous filaments being defined as a ratio of a total area of the continuous filaments visible within the pulp fiber-free spot region to the total surface area of the pulp fiber-free spot regions, determined from photographs of the spot regions.     
     
     
       2. The bio-degradable composite nonwoven fabric as claimed in claim 1, wherein the bio-degradable polyester filament nonwoven fabric is a spun bonded polyester filament nonwoven fabric having a basis weight of 5 to 30 g/m 2 . 
     
     
       3. The bio-degradable composite nonwoven fabric as claimed in claim 1, wherein the aliphatic dihydric alcohol is selected from the group consisting of alkylene glycols having 2 to 12 carbon atoms and cycloalkylene glycols and cycloalkylene-dialkanols each having 5 to 12 carbon atoms. 
     
     
       4. The bio-degradable composite nonwoven fabric as claimed in claim 1, wherein the dicarboxylic acid component comprises at least one member selected from the group consisting of malonic acid, succinic acid, adipic acid, suberic acid, sebacic acid, dodecanoic diacid, tartaric acid, malic acid, tetrahydroxysuccinic acid, tartronic acid and acetoxysuccinic acid. 
     
     
       5. The bio-degradable composite nonwoven fabric as claimed in claim 1, wherein the bio-degradable polyester filament nonwoven fabric layer has a plurality of filament-bonded portions in which the filaments are locally press-bonded to each other at the intersection points thereof. 
     
     
       6. The bio-degradable composite nonwoven fabric as claimed in claim 5, wherein the filament-bonded portions of the bio-degradable polyester nonwoven fabric layer each have an area of 0.03 to 4 mm 2 . 
     
     
       7. The bio-degradable composite nonwoven fabric as claimed in claim 5, wherein the filament-bonded portions of the bio-degradable polyester nonwoven fabric layer have a total area corresponding to 2 to 20% of to the total area of a surface of the composite nonwoven fabric. 
     
     
       8. The bio-degradable composite nonwoven fabric as claimed in claim 1, wherein the aliphatic polyester filaments have a thickness of 1 to 10 denier. 
     
     
       9. A process for producing the bio-degradable composite nonwoven fabric as claimed in claim 1, comprising the steps of: (1) forming a laminate comprising (A) a bio-degradable polyester filament nonwoven fabric consisting essentially of a plurality of continuous filaments comprising a bio-degradable aliphatic polyester which is a polymerization product of a glycol component comprising at least one aliphatic dihydric alcohol with a dicarboxylic acid component comprising at least one member selected from the group consisting of aliphatic dicarboxylic acids and hydroxyl and acetoxyl derivatives thereof, and superimposed on a support having a plurality of supporting protuberances spaced from each other, and   (B) a paper sheet comprising wood pulp fibers and superimposed on the bio-degradable polyester filament nonwoven fabric; and     (2) directing a plurality of water jet streams through nozzle openings toward the paper sheet surface of the laminate under a pressure sufficient to locally press the laminate against the supporting protuberances which do not allow the water jet streams to permeate therethrough, to penetrate the laminate and thereby to three-dimensionally entangle the pulp fibers and the continuous filaments with each other so as to convert the laminate to a composite nonwoven fabric, wherein the pressure applied to the water jet streams is also sufficient to force the pulp fibers distributed in portions of the pressed laminate located on and around the supporting protuberances to move to the circumferences of the pressed portions of the laminate, and the continuous filaments in the pressed laminate portions to move toward the circumferences of the pressed laminate portions, whereby a plurality of spot regions which are spaced from each other, are substantially free from the pulp fibers, and have a distribution density of the continuous filaments of 30 to 50%, an area of 0.16 to 16 mm 2  and a total area corresponding to 5 to 60% of the total surface area of the composite nonwoven fabric, are formed in the resultant composite nonwoven fabric, the distribution density of the continuous filaments being defined as a ratio of the total area of the polyester filaments visible within the pulp fiber-free spot region to the total surface area of the spot regions, determined from photographs of the spot regions.     
     
     
       10. The process as claimed in claim 9, wherein the water jet streams are spouted with a specific energy of 0.20 to 0.80 kWh/kg determined in accordance with the equation: ##EQU2## wherein E represents a specific energy in the units of kWh/kg of the water jet streams, A represents a total area in the units of m 2  of the nozzle openings for spouting the water jet streams therethrough, p represents a density in the units of kg/m 3  of water, g represents the acceleration of gravity in the units of m/sec 2 , P represents a pressure in the units of Pa of the water jet streams in the nozzle openings, M 0  represents a basis weight in the units of g/m 2  of the paper sheet, M 1  represents a basis weight in the units of g/m 2  of the bio-degradable polyester filament nonwoven fabric, S represents a speed in the units of m/min of the treatment for the laminate, and L represents a width in the units of m of the water jet-stream-treated portion of the laminate. 
     
     
       11. The process as claimed in claim 9, wherein the bio-degradable polyester filament nonwoven fabric has a basis weight of 5 to 30 g/m 2 . 
     
     
       12. The process as claimed in claim 9, wherein the continuous filaments for the bio-degradable polyester filament nonwoven fabric have a thickness of 1 to 10 deniers. 
     
     
       13. The process as claimed in claim 9, wherein the bio-degradable polyester filament nonwoven fabric has an average density of 0.10 to 0.15 g/cm 3 . 
     
     
       14. The process as claimed in claim 9, wherein the bio-degradable polyester filament nonwoven fabric has a plurality of filament-bonded portions in which the filaments are locally bonded to each other. 
     
     
       15. The process as claimed in claim 14, wherein each of the filament-bonded portions has an area of 0.03 to 4 mm 2 . 
     
     
       16. The process as claimed in claim 14, wherein the filament-bonded portions have a total area corresponding to 2 to 20% of the total area of a surface of the composite nonwoven fabric. 
     
     
       17. The process as claimed in claim 11, wherein the filament-bonded portions are formed by embossing the bio-degradable polyester filament nonwoven fabric at a temperature of 5° to 50° C. below the melting temperature of the aliphatic polyester under a linear pressure of 10 to 80 kg/cm. 
     
     
       18. The process as claimed in claim 9, wherein the paper sheet has a basis weight of 10 to 150 g/m 2 . 
     
     
       19. The process as claimed in claim 9, wherein the paper sheet has a density of 0.2 to 0.65 g/cm 3 . 
     
     
       20. The process as claimed in claim 9, wherein the paper sheet has a wet tensile strength of 0.04 to 15 kgf/25 mm. 
     
     
       21. The process as claimed in claim 9, wherein a ratio in basis weight of the paper sheet to the bio-degradable polyester nonwoven fabric is in the range of from 1:0.05 to 1:2. 
     
     
       22. The process as claimed in claim 9, wherein the support having a plurality of supporting protuberances is a coarse weave comprising a plurality of warps and wefts intersecting each other and having a plurality of throughholes defined by the warps and wefts, and the supporting protuberances are formed by the intersecting portions of the warps and wefts. 
     
     
       23. The process as claimed in claim 22, wherein the coarse weave has a warp density of 1.8 to 10 warps/cm and a weft density of 1.8 to 10 wefts/cm. 
     
     
       24. The process as claimed in claim 22, wherein the warps and wefts have a thickness of 0.5 to 2.0 mm. 
     
     
       25. The process as claimed in claim 9, wherein the support having a plurality of supporting protuberances comprises a base member and a plurality of protuberances projecting outward from the base member and having top faces spaced from each other. 
     
     
       26. The process as claimed in claim 25, wherein the base member is in the form of a drum and the protuberances are arranged on the peripheral surface of the drum. 
     
     
       27. The process as claimed in claim 25, wherein the base member is in the form of an endless conveyer and the protuberances are arranged on the peripheral surface of the endless conveyer. 
     
     
       28. The process as claimed in claim 25, wherein the protuberances have a height of 0.4 to 2.5 mm, and the top faces have an area of 0.16 to 16 mm 2 . 
     
     
       29. The process as claimed in claim 25, wherein the protuberances are arranged at regular intervals of 1.0 to 5.6 mm.